ADDomainController: Add ability to demote DCs with Ensure = Absent

[devopsjesus]

Details of the scenario you tried and the problem that is occurring

Issue #155 had the Ensure property added to the xADDomainController schema as a Read property, since there was no logic to support removing the DC role by setting Ensure to 'Absent'. This issue is a request to add that logic, and enable users to set the Ensure property by tagging it as a Write property.

Verbose logs showing the problem

n/a

Suggested solution to the issue

Add logic blocks to the Test- and Set-TargetResource functions to support removing the DC role from a target node.

The DSC configuration that is used to reproduce the issue (as detailed as possible)

xADDomainController Foo
{
    DomainName = 'contoso.local'
    DomainAdministratorCredential = $Password
    SafemodeAdministratorPassword = $Password
    Ensure = 'Absent'
}

The operating system the target node is running

Supported Windows Server

Version and build of PowerShell the target node is running

5.1+

Version of the DSC module that was used ('dev' if using current dev branch)

2.24

[johlju]

For reference, the cmdlet Uninstall-ADDSDomainController to demote a domain controller. I suggest we do not add parameters that ignores prerequisites or forcibly removes a domain controller, we should demote a domain controller the safest way possible with this cmdlet. 🤔